Clinical and experimental evidences show that disruption of the mechanism for middle ear (ME) pressure regulation is associated with pathophysiological changes including the development of significant under- pressures and mucosal inflammation that if prolonged results in otitis media with effusion (OME). Adequate regulation of ME pressure requires that the intermittent transient openings of the Eustachian tube (ET) provide a sufficient quantity of gas to balance the net glasses associated with the gradient driven exchange between the ME and blood. Poor ET function causes ME under-pressures and OME by the hydrops ex vacuo mechanism, the validity of which has been convincingly demonstrated in experiments conducted under this program. Indeed, treatments for OME that bypass the ET to supply the ME with gas were shown in clinical trials to promote disease resolution. ET function tests in children and adults with concurrent diseases that predispose them to OME show changes in intraluminal congestion that present as a decreased efficiency of the muscular assisted mechanism of tubal dilation. Other studies in children "t risk" for OME and with concomitant OME, show a primary impairment of the active mechanism for tubal openings. However, the prognostic value of ET function tests with respect to disease course is limited, provoking controversy as to the role of ET dysfunction in the pathogenesis of OME. Recent studies conducted under this program show that the discordance between disease progression and test results may be explained by the failure of current test protocols to assess concurrently the functional demand placed upon the ET by the varying rates of transmucosal gas exchange. The overall objective of this project is to develop clinically applicable tests for ME pressure regulation that assess simultaneously these demand and supply functions. Also evaluated is the effect of measured test parameters associated with mucosal healing. Because histopathological studies cannot demonstrate an anatomic basis for poor ET function, new MRI imaging techniques will be used in an attempt to relate in vivo ET structure and function. The goals of this project are to develop a better understanding of ME pressure-dysregulation in the pathogenesis of OME, to evaluate the prognostic value of newly developed test protocols for assessing that function, to identify the underlying cause(s) of ET dysfunction, and to utilize this knowledge in suggesting new treatment strategies for OME..